1. Field of the Invention
This invention relates to surface-acoustic-wave (SAW) components, which are adapted to electronic circuits and devices such as filters and oscillators. In addition, this invention also relates to manufacturing methods of oscillators using surface-acoustic-wave components.
This application claims priority on Japanese Patent Application No. 2003-20803, the content of which is incorporated herein by reference.
2. Description of the Related Art
Recently, demands for developing surface-acoustic-wave components and electronic devices using them have been rapidly increased due to remarkable expansion and development of communication fields in mobile communications using cellular phones and the like. Surface-acoustic-wave components have been developed by using single crystals such as quartz crystals, whereas in consideration of recent progresses of electronic devices that are driven at higher frequencies and are produced using highly integrated semiconductor components, it is strongly demanded that surface-acoustic-wave components using piezoelectric thin films be further advanced.
Conventionally, various types of surface-acoustic-wave components using piezoelectric thin films have been developed. For example, Japanese Patent Application Publication No. Hei 7-50436 discloses an example of a surface-acoustic-wave component in which a zinc oxide (ZnO) piezoelectric crystal film is formed on a sapphire substrate; and Japanese Patent Application Publication No. Hei 1-103310 discloses an example of a surface-acoustic-wave component in which a piezoelectric film is formed on a diamond-like carbon film layer formed on a Si substrate. In addition, an example of a surface-acoustic-wave component in which a lithium niobate (LiNbO3) thin film is formed on a sapphire substrate is disclosed in the monograph entitled ‘Epitaxial growth and surface-acoustic-wave properties of LiTaO3 films grown by pulsed laser deposition’ published in Applied Physics Letters, Vol. 62 (1993), pp. 3046–3048.
Integrating the aforementioned surface-acoustic-wave components on silicon substrates together with semiconductor components is useful in reducing sizes of devices using surface-acoustic-wave components and in actualizing high performance in devices using surface-acoustic-wave components. For example, Japanese Patent Application Publication No. Hei 6-120416 discloses that a surface-acoustic-wave component comprising a single crystal is joined onto a silicon substrate forming a semiconductor component.
The conventional technology regarding the aforementioned surface-acoustic-wave components has the following drawbacks.
That is, when a zinc oxide thin film or a lithium niobate thin film is formed on a sapphire substrate, it is very difficult to form a semiconductor component such as a complementary metal-oxide semiconductor (CMOS) component on the sapphire substrate.
It may be possible to form a zinc oxide thin film on a silicon substrate; however, an electromechanical coupling coefficient (hereinafter, denoted as ‘K2’) of zinc oxide is very low. Therefore, when a surface-acoustic-wave component is adopted in a high-frequency filter, it may be ideal to use a prescribed material having a higher value of K2 such as lithium tantalate (LiTaO3) and lithium niobate (LiNbO3) in order to produce a desired transmission band, i.e., a relatively broad frequency band; however, it is very difficult to form an orientation film having a good quality on the silicon substrate.
When a zinc oxide thin film is formed on a diamond-like carbon film formed on a silicon substrate, it is very difficult to form a semiconductor component on the diamond-like carbon film. Similar difficulty occurs even when a thin film composed of another material such as lithium niobate and lithium tantalate other than zinc oxide is formed.
When a surface-acoustic-wave component comprising a single crystal is joined onto a silicon substrate on which a semiconductor component is formed, there is a problem in that characteristics of the surface-acoustic-wave component are greatly influenced by cutting angles of a single crystal plate.